The present invention relates generally to semiconductor packaging. More specifically, the present invention relates to the packaging of semiconductor devices having a reduced incidence of burring at its contacts.
Semiconductor integrated circuits (IC""s) are typically fabricated in wafer form. After fabrication, individual die are cut from the wafer and then packaged. Generally, many die are packaged simultaneously on a metal lead frame. A lead frame includes tie bars which support an array of die attach pads and contacts which are associated with each die attach pad. A die is mounted onto each die attach pad and electrically connected to the associated contacts. The contacts provide the physical connection between the input and output terminals of the die and those of the circuit board. A molding material is then applied to encapsulate the die and the non-contact surfaces of the contacts. The molding material serves to protect the IC and makes it easier to handle. After the molding compound is applied, each packaged die is cut from the molded lead frame (e.g. xe2x80x9csingulatedxe2x80x9d) and is then ready to be mounted onto a circuit board.
Generally, singulation is performed by guiding a circular saw blade along the tie bars of the lead frame. As the cutting surface of the saw blade cuts through the lead frame and the molding compound, the sides of the saw blade, through frictional force, may pull some of the metal contact material above the contact surface of the contacts. This metal contact material thereby forms a thin sliver of metal, called a xe2x80x9cburr,xe2x80x9d on the contact surface of the contact. Burrs may separate from the contacts while mounting the packaged die onto a circuit board. These free-floating burrs may cause the system on the circuit board to malfunction due to faulty connections or xe2x80x9cshort-circuits.xe2x80x9d Quality assurance procedures aimed at minimizing such problems adds to the cost and complexity of the packaging process.
In view of the of the foregoing, a semiconductor device exhibiting a lower incidence of burrs forming on its contacts during the singulation process would be desirable.
The present invention relates to a semiconductor device exhibiting a lower incidence of burrs forming on its contacts during the singulation process. The semiconductor device includes a die which is electrically connected to a set of associated contacts wherein each contact has a contact surface and a non-contact surface. Each contact surface of the contacts contains a recessed region filled with a first deposit of molding material. The die and the non-contact surfaces of the contacts are encapsulated with a second deposit of molding material.
The semiconductor device is singulated from a molded lead frame by guiding a saw blade through the recessed regions formed on the contact surface of the contacts. The molding material in the recessed regions creates a xe2x80x9cbuffer zonexe2x80x9d which separates the path of the saw blade from the contact surface of the contacts. As a result, the formation of burrs is reduced because the sides of the saw blade are no longer in contact with the contact surface and are therefore unable to pull the contact surface into a burr formation. The molding material also prevents the contact material at the bottom of the recessed region, on the newly cut surface of the contact, from being pulled above the contact surface of the contact. The molding material in the recessed region accomplishes this by acting as a barrier which blocks the movement of contact material which may be pulled. Additionally, any contact material which is pulled towards the contact surface becomes lodged in the molding material, thereby failing to reach the contact surface of the contact.
In sum, this invention results in a semiconductor device exhibiting a lower incidence of burrs forming on its contacts during the singulation process. This invention thereby minimizes the occurrence of faulty electrical connections upon the mounting of packaged die onto circuit boards and reduces the extent and cost of procedures aimed at detecting burrs.